According to the blog post, you can visualize that number by thinking about the total number of people on earth about "three to four millennia ago."

Well, the world certainly has changed a lot since then. Today, we have seven billion people on Earth, and there are centers of commerce almost everywhere. With changes in technology and mechanized forms of transportation, letters (surprisingly) still takes days to get from person to person, while email takes just seconds.

But one of the biggest changes is one we reached today - when 40 million concurrent users were signed onto Skype all at once. This is a massive new milestone for a simple piece of software that helps make meaningful connections a cool part of people's lives every single day.

Tony Bates, President of the Skype Division at Microsoft had this to say: